1. Technical Field of the Invention
The present invention relates to rotors for vehicle alternators and, more particularly, to a rotor of a vehicle alternator adapted for installation on automotive vehicles and trucks, etc.
2. Description of the Related Art
In general, a vehicle alternator rotor has cooling fans provided with fan blades on which a centrifugal force acts. When this takes place, the fan blades bear a centrifugal force, resulting from the rotation of the rotor, which acts in a radial direction to cause the fan blades to warp backward in a direction opposite to the fan blades. In a case where the fan blades are reliably joined to magnetic pole pieces (claw-shaped pole pieces) at axially outward end faces thereof, the occurrence of such warping can be suppressed with the use of a reactive force of the claw-shaped pole pieces.
In reducing fan noise, further, the fan blades have been located at circumferentially unequaled intervals (see, for instance, Patent Publication 1: Japanese Patent No. 3876912 on pages 3-5 and in FIGS. 1-3). With the fan blades located at the circumferentially irregular intervals, there is a risk of the fan blades coming into contact with parts of the claw-shaped magnetic poles. In order to allow such fan blades with low strength to have strength for withstanding the centrifugal force, an attempt has been made to employ a method of forming the fan blades in decreased sizes with an undesired result because of a drop in cooling capacity. With the technology disclosed in Patent Publication 1, the cooling fan has base portions (fan bases) provided with front and rear fixing portions that are devised to ensure the fan blades to have increased fixing strengths.
Meanwhile, with the rotor for the vehicle alternator disclosed in Patent Publication 1, an attempt has been made to devise suitable positions of the fixing portions of the fan bases. However, there is likelihood that the positions of the respective fixing portions cannot be necessarily located in positions as disclosed in Patent Publication 1 in light of restrictions on products. Further, the rotor, disclosed in Patent Publication 1, has cutout portions formed in parts of the fan bases at areas radially inward of the fan blades. When subjected to the centrifugal force, an issue arises with the fan blades caused to deform accompanied by stress acting on the cutout portions, depending on orientations or lengths of the cutout portions, resulting in a drop in strength of the cooling fan. Another issue arises with the occurrence of the fan blades having increased deformations. For a vehicle alternator of a small size rotatable at a high speed, the deformation of each fan blade needs to be reduced to be less than a gap between a stator and the rotor.